Three other officials, including Bryansk Deputy Mayor Vladimir Voronin, have previously resigned of their own free will following the incident, which saw ground in a pedestrian zone literally open up beneath a young mother with a baby carriage.

The woman managed to hold on to a pipe sticking out of the two-by-four-meter hole and was pulled out by her policeman husband, who promptly arrived on the scene.

But she failed to hold on to the carriage with their toddler son, who fell into the depths of the three-meter-deep hole and was swept away by a stream of sewage at the bottom. His body was found the next day five kilometers away from the hole.

Investigators tentatively blamed the collapse on violations during construction of the sewage tank, but Bryansk City Hall pointed to gas corrosion corrupting sewer pipes.

The regional branch of the Investigative Committee opened a case on manslaughter by professional negligence, punishable with up to three years in prison, but did not press any charges as of Thursday.

Utilities systems throughout the country are old and growing increasingly decrepit. Ten similar incidents were reported across Russia between 2010 and 2011, one ending in a fatality and another temporarily robbing 260,000 residents of Rostov-on-Don of access to clean water, RIA-Novosti said.